Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by IC engines. Generally exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust gas aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) system including a catalyst formulated to convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O) in the presence of ammonia (NH3). Generally in such aftertreatment systems, an exhaust reductant, (e.g., a diesel exhaust fluid such as urea) is injected into the SCR system to provide a source of ammonia, and mixed with the exhaust gas to partially reduce the NOx gases. The reduction byproducts of the exhaust gas are then fluidically communicated to the catalyst included in the SCR system to decompose substantially all of the NOx gases into relatively harmless byproducts which are expelled out of the aftertreatment system.
An exhaust reductant is generally inserted into the SCR system as the source of ammonia to facilitate the reduction of constituents such as NOx gases of the exhaust gas (e.g., a diesel exhaust gas). Pumps are often used to insert the reductant into the SCR system. Generally such pumps include mechanical pressure relieve valves which passively activate to relieve pressure and prevent excessive pressure buildup in the pump. Pressure relief valves often malfunction or fail and have to be replaced, which significantly adds to the maintenance cost of such systems.